May be okay during the week at some of the main beaches, although with university on break I would imagine they will not be deserted (my experience from UCSB a few years back now). Also, I've read accounts in recent years of rangers ticketing nudies at More Mesa (please... what a waste of taxpayers $$$), so discression would certainly be advised from that perspective.

Another alternative is to explore some of the more secluded beaches north of SB towards Gaviota. Haven't visited myself, but there never appeared to be more than a few cars by the side of the road for these and I'm sure you would have all the seclusion you need for a beach triste. Just depends on whether the possibility of being 'caught' is part of the thrill! ;-)

Bear in mind that I haven't been back to SB since '95, so my advice may be a tad beyond the expiry date!